1. Field of the Invention
The present invention relates to a signal processing method which is suitable in the case where data for the computer is recorded to an optical disc or the case where such data recorded on an optical disc is reproduced.
2. Description of the Prior Art
As a memory medium for recording a digital video signal which has been compressed by an MPEG (Moving Picture Experts Group) technique or the like, a DVD (digital video disc) has been developed. The DVD is an optical disc which has the same diameter as that of a CD (compact disc) and in which recording density has been further improved by progress in realization of a short wavelength laser beam, an increase in numerical aperture NA of an objective lens, and an improvement in processes for digital modulation and error correction encoding. Even in the case of a single-layer disc, the DVD has an extremely large data memory capacity, for example, about 3.7 Gbytes. As a form of DVD, there has been proposed a disc which is recordable and reproducible by using an MO disc or a phase-change type optical disc in addition to a read only optical disc.
It has been proposed that such a DVD be used as an external memory device of a computer. That is, as an external memory device of the computer, an optical disc drive has advantages such as large capacity and high-speed access. A CD-ROM and a CD-I (CD-Interactive) constructed in a manner such that data is recorded to a CD, MD (mini disc) data which is recorded and reproduced to/from an MD (mini disc), and the like have already been proposed. Since the DVD has an extremely large data memory capacity of about 3.7 Gbytes, the DVD can act as an external memory medium of larger capacity.
In the DVD, in order to protect recorded data, an error correction encoding process is performed. Since sequential data such, as video data, is handled in the DVD, a cross interleave code of a convolution type is used. However, when the convolution code is used, it is difficult to access the data on a sector unit basis and to read and write the data. In the case where the DVD is used as an external memory medium for recording and reproducing computer data, it is necessary to access the data on a sector unit basis and to read and write the data, so that it is necessary to use a code of a block completion type.
FIG. 9 shows an example of generating the convolution type cross interleave code. As shown in FIG. 9, a parity P of, for example, eight bytes is added to, for example, 162 bytes in the vertical direction in a C1 sequence. In a C2 sequence, a parity Q of, for example, 14 bytes is added in the oblique direction. By adding data of 148 bytes in the vertical direction, parity P of 8 bytes, parity Q of 14 bytes, the number of data bytes in the vertical direction is equal to 170 bytes. The data recorded on the disc is read out therefrom synchronously with the frame. One frame is equal to 85 bytes. The data of 170 bytes in the vertical direction is equal to two frames.
As mentioned above, although the convolution type cross interleave code is used in the DVD, it is difficult to access every block of the data and read and write the data by using the convolution type code. A cross interleave code of the block completion type has, therefore, been proposed.
FIG. 10 shows an example of processes in the case of generating the block completion type cross interleave code. In order to realize a common construction with the case of the above-mentioned convolution code, the number of data bytes in the vertical direction is set to 148 bytes, the parity P is set to eight bytes, the parity Q is set to 14 bytes, and the total number of data bytes in the vertical direction is set to 170 bytes. Since one sector is set to, for example, 16 kbytes, the number of data bytes in the horizontal direction is set to 112 bytes (148xc3x97112=16576 bytes). When the block completion type cross interleave code is used, a length of interleave is longer than a width of the block. Therefore, as shown in FIG. 10, when the number of data bytes in the horizontal direction reaches the length of 112 bytes, an aliasing of the C2 sequence occurs. As shown in FIG. 10, when the block completion type cross interleave code is used, data can be read and written at every block such that it is suitable for a case where the DVD is used as an external memory medium for recording and reproducing data for the computer.
As a sector size in the case where data is recorded and reproduced to/from a data recording medium such as a DVD or the like becomes large, the disc can meet requirements for high density and high reliability. In association with it, the file size to be handled becomes larger. Therefore, in recent years, there is a tendency to increase the sector size of data recording medium such that the size of one sector has been changed from an initial 512 bytes to 1024 bytes and, further, to 2 kbytes.
However, since the access to the recording medium is performed on a sector unit basis, as the sector size becomes larger, it takes a long time for reading and reproducing. There is, consequently, a problem such that an accessing speed including error correction encoding and decoding processes decreases. In addition to the problem of compatibility with a sector of an existing data recording medium, there is a further demand for a small sector.
In the case of recording data to the DVD, however, when the number of sectors is reduced, the reliability of the data deteriorates.
That is, in the above-mentioned example, the sector size is set to 16 kbytes. When the sector size is set to 16 kbytes, as shown in FIG. 10, an aliasing of the C2 sequence occurs once.
Since the block shown in FIG. 10 has 16 kbytes, when such a block is divided into eight portions, a sector of 2 kbytes can be constructed. However, as shown in FIG. 11, when the block of 16 kbytes is divided into eight portions to form each sector of 2 kbytes (14xc3x97148=2072 bytes) and the error correction encoding is performed by using the cross interleave code in a manner similar to the foregoing example, many aliasings occur in the C2 sequence. Thus, sufficient error correction cannot be performed.
As mentioned above, when the sector size is increased, although the reliability of data is improved, there is a drawback because the accessing speed becomes slow. On the contrary, when the sector size is reduced, although the accessing speed is raised, there is a drawback because the reliability of data deteriorates.
It is, therefore, an object of the invention to provide a recording and reproducing method whereby a sector of a small size can be accessed and an accessing speed can be raised while maintaining a reliability of data.
According to the invention, there is provided a data recording method whereby an address signal is recorded to a disc for every sector, data is arranged in an error correction encoding block and is subjected to an error correction encoding process, the error correction encoding block is divided into a plurality of portions in a predetermined direction to thereby form sectors, and the data of each sector is recorded in correspondence to the address signal.
According to the invention, there is provided a method of reproducing data from a disc in which an address signal for each sector has been recorded and data of each sector has been recorded in correspondence to the address signal, wherein the data of each sector is formed by dividing an error correction encoding block into a plurality of portions in a predetermined direction, the address signal of the disc is detected, the data is reproduced for every sector, an error correcting process is executed for the reproduced data in the sector, and when errors cannot be corrected by the error correcting process in the reproduced data in the sector, an error correction block including such a sector is reproduced, and the error correcting process is performed for the reproduced data in the error correction block.
A header is recorded at every predetermined sector interval on the disc. The address signal is included in the header. Recording data is arranged in an error correction encoding block and an error correction encoding process is performed. The error correction encoded block is divided into a plurality of portions in a predetermined direction, thereby forming sectors. Subsequent to the header, the data of each sector is recorded. Since the sector is formed by dividing the error correction encoded block into a plurality of portions in the predetermined direction, when the error correction encoding is performed in two directions by the error correction encoding blocks, one of the error correcting processes can be executed in each sector. Upon reproduction, the header is detected and the data is reproduced for every sector. One of the error correcting processes is executed in the reproduced data in the sector. When the errors cannot be corrected by the error correcting process in the reproduced data in the sector, the error correction block including such a sector is reproduced. The error correcting processes are executed in the sequences in the two directions. By using the above method, a sector of a small size can be handled without a deterioration of the reliability of data.
The above and other objects and features of the present invention will become apparent from the following detailed description and the appended claims with reference to the accompanying drawings.